Not Applicable
Not Applicable
Not Applicable
The present invention relates to electronic compasses of the type mounted on a dash or headliner of a vehicle for providing a continuous readout of the vehicle heading during operation.
In service, problems have been encountered with electronic compasses in vehicles during the initial calibration and subsequent calibration attempts. A known procedure for automatically recalibrating the compass during operation is that shown and described in U.S. Pat. No. 5,390,122 issued in the name of P. A. Michaels, et al which describes a procedure for initially calibrating the compass on the vehicle assembly line during manufacture and references an alternative way by driving in circles and describes a way of automatically calibrating the compass to update the calibration coefficients of the sensors.
In the aforesaid initial calibration of an electronic compass for vehicles, care must be exercised when measuring the magnetic field during the assembly of the vehicle to determine the proper offsets to calibrate the compass module. Typically in an automotive vehicle assembly plant, the equipment on the vehicle assembly line is metallic and affects the nearby earth magnetic field. Typically, a certain designated area is used for compass calibration; however, if any of the equipment is moved in the designated area, the factory calibration of the compass may be affected and result in inaccurate initial calibration. If this occurs, the magnetic field in the designated calibration area must be re-measured and new calibration offsets determined.
The known technique for recalibrating a compass requires that the car be driven in the four cardinal directions (i.e., N, E, S, W) in sequence and at a fixed or constant rate before a complete set of corrections can be applied.
It has been desired to provide a way or means of providing a rapid automatic calibration or recalibration of an electronic compass for a vehicle during normal driving.
The present invention provides accelerated calibration of an electronic compass for vehicle of the type employing magnetoresistive sensors. The system may be activated by a user operated panel switch or by a condition developing with a known slow automatic calibration routine in the event that the system detects that it has been forced into an unrecoverable state. The accelerated calibration technique of the present invention does not require the driver to drive in any set pattern such as a circle: it only requires that the four cardinal headings be visited at least once.
The accelerated or fast automatic calibration technique of the present invention detects and records high and low peaks in the output of the magnetoresistive sensors detecting respectively Forward and Lateral variations in the combination of remnant and Earth magnetic fields over time. The technique of the present invention eliminates the need for the vehicle to be driven in the four cardinal directions in sequence and at a constant rate in order to complete the compass model in the computer. The technique of the present invention is initiated when it is determined that the vehicle has been driven in an arc sufficient to generate a minimum threshold change in the output of both the Lateral and the Forward magnetoresistive sensors, whereupon the system models an arc and computes the center of curvature as the center of the locus in order that the current quadrant can be determined. A xe2x80x9cboxxe2x80x9d is then calculated with the computed center computed for determining the four quadrants as contrasted with cardinal headings. The xe2x80x9cboxxe2x80x9d is updated with each sampling and when the vehicle has, over time, been driven in all quadrants, the model is complete. The xe2x80x9cboxxe2x80x9d will always contain the circle of the peaks of the sensor outputs from all four cardinal directions. The mapped circle is then shifted to be located within the limits of the outputs of the system amplifiers such that saturation is avoided; the compass readings detected are thus valid for determining headings and are not unduly influenced by the remnant magnetic fields.